CAIRO (Reuters) - Egyptians vote this weekend on constitutional changes that will potentially allow President Abdel Fattah al-Sisi to stay in office until 2030 and bolster the role of Egypt's powerful military.

Sisi's supporters say the changes are necessary to give him more time to complete major development projects and economic reforms. Critics say they concentrate more powers in Sisi's hands and return Egypt to an unequivocally authoritarian model.

Egypt's 596-member parliament, dominated by Sisi's supporters, approved the amendments on Tuesday, voting by 531 to 22 in favor.

Some 55 million of Egypt's nearly 100 million population are eligible to cast votes in the referendum, which will be held over three days starting on Saturday.

While the changes are widely expected to pass, observers say the size of the turnout will be watched as a test of Sisi's popularity, which has been dented by economic austerity measures since 2016.

Opponents of the changes complained that they were being rushed through without proper public scrutiny.

"They are not giving us time to even organize a campaign to ask people to vote no," said Khaled Dawoud, a member of the opposition Civil Democratic Movement, which has rejected the changes.

"This is the final deathblow after all the ambitions we had after the 2011 revolution," said Dawoud, referring to the uprising that ousted veteran leader Hosni Mubarak. Dawoud said campaigning would take place online due to the lack of time.

Egyptian officials have said that Egyptians from all walks of life were given a chance to debate the amendments, and that all views were factored into the final proposals.

"LEAVE IT TO GOD"

If approved, the amendments would extend Sisi's current term to six years from four and allow him to run again for a third six-year term in 2024.

They would also grant the president control over appointing head judges and the public prosecutor from a pool of candidates. They would task the military with protecting "the constitution and democracy and the fundamental makeup of the country and its civil nature".

Banners urging Egyptians to participate in the referendum sprang up in Cairo this month before the final version of the amendments was known or voted on by parliament. Some of the signs encourage people to vote yes.

"Vote? Vote for what?" asked a horse carriage driver sitting at a cafe in a working class Cairo neighborhood.

"It won't make a difference," said the 67-year-old, who declined to give his name. "Leave it to God."

Sisi came to power after spearheading, as defense minister, the removal of the Muslim Brotherhood's Mohamed Mursi as president in 2013, and winning election a year later. He was elected to a second four-year term last year.

Under Sisi, Egypt has witnessed a crackdown on dissent that rights groups say is unprecedented in its recent history. Media and social media are tightly controlled.

Lina Khatib, head of Chatham House's Middle East and North Africa Programme, said the amendments "pave the way for a power grab" by Sisi.

"This has grave implications for prospects of democracy in Egypt in the medium term and makes it difficult for alternative political voices to contest power in the long term," she said in an emailed comment to Reuters.